Endoprosthesis components used to replace parts of the human skeleton must satisfy a number of requirements. The endoprosthesis component has to be sufficiently stable to ensure that it can take up the forces that occur in the skeleton. In addition, those elements of the endoprosthesis component that are in contact with the tissue, including bone substance, of the human body in the implanted state must have good biocompatibility.
It is already known for surface portions of the endoprosthesis component that are designed for contact with human tissue to be covered with a layer composed of a hard material, for example a nitride, an oxynitride or an oxide based on a refractory metal. Hard material coatings of this kind combine good mechanical properties together with good biocompatibility.
However, problems occasionally arise concerning the acceptance of such endoprosthesis components by the human body. For example, microorganisms may attach themselves to the surface of the endoprosthesis component and in so doing hinder the acceptance of the endoprosthesis component in the human body. The risk of microorganisms on the surface of endoprosthesis components is greater, the more invasive the procedure needed to implant the endoprosthesis component into the body, and the greater the surface area across which the endoprosthesis component comes into contact with the tissue of the body. Operations in which an invasive procedure is needed, and in which the endoprosthesis is brought into contact with human body tissue across a large surface area, are, for example, head/shaft prosthesis shafts, or those in which the femur is replaced completely by an endoprosthesis.
It is known from WO 03/094774 to oxidize the surface of an implant, made of metal or a metal alloy, and to provide the resulting hard material layer with silver particles in order to obtain an antimicrobial action. Since hard material layers react only very slowly with the surrounding body tissue, the silver particles are released from the hard material layer over a long period of time. A hard material coating of this kind can therefore provide good long-term action. Directly after insertion of the implant, however, a large number of microorganisms may be present in the environment of the implant. The quantity of silver particles released by the hard material layer is too small to be effective against a larger number of microorganisms.